To fasten an object W such as furniture or wooden articles, referring to FIG. 1A and FIG. 1B, a screw 1 with a tip portion 11 at the distal end is commonly used. As the object W usually does not have a hole formed by drilling in advance, the tip portion 11 has to be screwed into the object W by force during tapping of the screw 1; meanwhile, chips are generated by means of threads 12 of the screw 1 and then channeled out reversely along the threads 12. While the threads 12 are wedged in a screw hole W1 of the object W during tapping, the chips easily clogs the threads 12 to generate frictional resistance. Hence fastening the screw 1 requires a greater effort, and the screw hole W1 tends to be squeezed to generate cracks C1 to result in damage of the object W. This weakens the strength of the object W and reduces the durability thereof. It also spoils the appearance of the object W. Moreover, after the screw head 13 of the screw 1 is wedged in the screw hole W1, the screw hole W1 also is squeezed by the screw head 13 to create other cracks C2.